297. Serialize and Deserialize Binary Tree

At a Glance

• Topic: String
• Pattern: Analyze Pattern
• Difficulty: Hard
• LeetCode: 297

Problem Statement

Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or transmitted across a network connection link to be reconstructed later in the same or another computer environment.

Design an algorithm to serialize and deserialize a binary tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure.

Clarification: The input/output format is the same as how LeetCode serializes a binary tree. You do not necessarily need to follow this format, so please be creative and come up with different approaches yourself.

Example 1:

Input: root = [1,2,3,null,null,4,5] Output: [1,2,3,null,null,4,5]

Example 2:

Input: root = [] Output: []

Constraints:

The number of nodes in the tree is in the range [0, 104].
-1000 <= Node.val <=...

Approach & Solution Steps

Use Preorder Traversal (DFS). Serialize to a string using commas to separate values, and use 'N' for null nodes. For deserialization, split the string by comma and use a recursive function with a queue to rebuild the tree.

Optimal JS Solution

var serialize = function(root) {
  const res = [];
  function dfs(node) {
    if (!node) {
      res.push('N');
      return;
    }
    res.push(node.val);
    dfs(node.left);
    dfs(node.right);
  }
  dfs(root);
  return res.join(',');
};

var deserialize = function(data) {
  const vals = data.split(',');
  let i = 0;
  function dfs() {
    if (vals[i] === 'N') {
      i++;
      return null;
    }
    const node = new TreeNode(Number(vals[i]));
    i++;
    node.left = dfs();
    node.right = dfs();
    return node;
  }
  return dfs();
};

Edge Cases & Pitfalls

• Always consider empty or null inputs.
• Watch out for off-by-one index errors.